Over the years, much interest has been directed towards devising a means to produce good quality three-dimensional photographs. A number of schemes have been put forward. One system representative of these is disclosed in U.S. Pat. Nos. 3,482,913 and 3,504,059 to Glenn. Described therein is a technique wherein a plurality of cameras are located sequentially in a horizontal line to record images of a scene from differing viewpoints, which when assembled and viewed with a lenticular lens sheet, yield a stereoscopic view of the scene originally photographed. This sytem, called "lenticular photography" has the drawback that the lenticular lens sheet must be overlayed on the composite photograph for viewing. It also suffers from shallow field of view and "view flipping".
Recently, with the advent of lasers as a readily available source of coherent light, holograms have gained favor as the preferred means to create three-dimensional recordings of scenes. Unlike a conventional photograph, which is a recording only of light intensities reflecting off the surface of an object, a hologram records the curvature and relative orientation of the wavefronts of the reflected light off the object, as well as the intensities. This is accomplished by recording an interference pattern of the reflected light in relation to a reference beam of light. The resulting holographic recording contains all the information about the object necessary for viewing it in three-dimensional perspective. An excellent treatment of the various schemes to create three-dimensional photographs can be found in "Three Dimensional Displays", by T. Okoshi, Proc. IEEE 68, 548 (1980), hereby incorporated by reference.
First developed by Leith and Upatnieks at University of Michigan, early laser holography was accomplished in a laboratory under very high interferometric precision. In this scheme, a laser beam is split in two, one beam, called an object beam, is directed to illuminate an object, the light then reflecting to a holographic plate, the other beam, called a reference beam, is directed directly toward the photographic plate at an angle relative to the first so as to produce interference between the wavefronts of the beams at the plate. The resulting interference pattern between the beams is recorded on the plate, forming a hologram. The hologram so produced can be viewed from different angles, each revealing a different perspective of the object recorded with a parallax effect similar to what would be seen by looking at the object itself. A detailed description of holography, and its development, is contained in the book "Optical Holography" by R. Collier, C. Burckhardt and L. Lin, Academic Press, 1971.
Holography utilizing laser light to illuminate the object and expose the holographic film has several drawbacks: It is practical only for recording relatively small objects, close-up, indoors in a controlled environment, with expensive and potentially dangerous lasers. Several attempts have been made to overcome these limitations so that holographic recording of scenes of all kinds may be more easily and safely accomplished. These schemes involve the concept that a scene may be photographed in incoherent light from various viewpoints and in so doing record a large quantity of information concerning the objects in the scene, as suggested by Glenn, then using the information contained on the resulting images, to produce, with coherent light, a hologram having three-dimensional parallax.
Such a scheme was proposed by R. V. Pole in a scientific paper, App. Phy. Lett. 10, 20, 1967, hereby incorporated by reference and later in U.S. Pat. No. 3,515,452, hereby incorporated by reference. Therein he described a method to utilize a fly's eye lens array placed over a photographic plate for "spatially sampling" the object. The recording from the fly's eye lens is called an "integral photograph", an old technology in which the recording behind each lenslet is a miniature image of the object from that perspective viewpoint. Pole's "Holocoder" scheme includes both the "integral photograph" and the steps to convert it into a hologram. When the holographic film is developed, and put in its original position with illumination in the reverse direction, a truly three-dimensional image may be seen. If coherent light is used to illuminate the integral photograph, it may then be used as the object to record a hologram, the integral photograph substituting for the objects in the scene itself. Thus, the scene may be conveniently recorded in incoherent light, then the resulting integral photograph processed precisely in coherent light to produce a hologram. The disadvantage of this system is that a good quality fly's eye lens array is very difficult to fabricate, resulting in relatively poor optics. Additionally, there is no provision for focusing, each lens in the array having a very short fixed focal length in all directions. Also, there is a screen effect resulting from the lens array which yields a dot matrix appearance. Further, optical noise is focused by the array, becoming quite noticeable and objectionable. Finally, there is a very narrow field of view which results from the limited size of the lens array. These disadvantages have prevented the holocoder process from becoming successful. Others have attempted to improve on Pole's concept, with only limited success:
U.S. Pat. No. 3,598,484 to Redman, hereby incorporated by reference, discloses a "multiplexing" system to obtain a hologram from a series of photographs having differing perspective information. In this approach, a series of varied angle photographs are taken, developed into transparencies, then illuminated with coherent light in conjunction with angling the holographic plate to coincide with the original angle of the camera at the time of photographing the scene. This system requires precise alignment of the apparatus during a complicated series of holographic plate and transparency movements while assembling the multiplex hologram.
U.S. Pat. No. 3,608,993 to DeBitetto, hereby incorporated by reference, describes a linear lens array instead of the substantially square fly's eye lens matrix of Pole. This is used to reduce vertical parallax information, while retaining horizontal parallax information. A film stepping apparatus is needed to advance the holographic film vertically so that a composite hologram of parallel identical strips may be fabricated. The process is thus tedious and complicated and does not solve the problems indicated above in regard to the holocoder approach.
U.S. Pat. No. 3,765,741 to Kimura et al, hereby incorporated by reference, discloses the use of a horizontal lens array which is used to photograph a scene yielding only horizontal parallax information. Using this lens in combination with the photograph, the scene is projected on a screen and thereupon imaged through a fly's eye lens array and a second photograph is taken. Then laser light entering the fly's eye lens from the rear shines onto a holographic plate, forming a hologram. This system is extremely complicated.
U.S. Pat. No. 3,884,545 to Kasahara et al, hereby incorporated by reference, discloses the use of a matrix of high quality optical lenses instead of the closely spaced fly's eye lenses of Pole, effecting an improvement in the optics.
U.S. Pat. No. 3,985,419 to Matsumoto et al, hereby incorporated by reference, discloses a holocoder system where the invention is the inclusion of a diffusion screen, acting as a light scatterer, in combination with the multiple lens system to cause the images to be formed on the holographic plate reconstructing the image of the entire pupil of the imaging system. Scatterers are disclosed in earlier U.S. Pat. Nos. 3,608,993, 3,765,741 and 3,884,545, referenced above. In this method, there remains all the problems encountered with the Pole method, except that the imaging is enhanced due to use of the diffuser.
U.S. Pat. No. 4,039,245 to Yano, hereby incorporated by reference, shows a system in which a composite hologram is formed by use of a projector lens for each of a series of two-dimensional photographs. Coherent light having passed through the photograph-lens combinations reaches a screen, which could be a lenticular lens array with a diffusion reflecting surface behind it, where each lens element disperses light in one orthogonal direction and redirects light in the other orthogonal direction so as to cause images from each photograph to appear at differing points on the holographic plate. This concept utilizes high quality projector optics, but the process is complicated and elaborate.
U.S. Pat. No. 4,445,749 to Benton, hereby incorporated by reference, shows a system in which a hologram is constructed from a number of two-dimensional photographs by means of a recording system in which a series of strip holograms are formed by use of a mask which exposes strips of a holographic plate sequentially from one side to the other as each two-dimensional photograph is individually illuminated. The resulting hologram is in turn illuminated as the object for exposure of another holographic plate, forming the final hologram.
In the scientific journal literature, D. J. DeBitetto describes an approach to reduce vertical parallax information using strip hologram techniques in his articles in Appl. Phy. Lett. 12, 343, 1968 and Appl. Opt. 8, 1740, 1969, both articles hereby incorporated by reference. Generally, he discloses the underlying principles of the above referenced U.S. Pat. No. 3,608,993.
Applicant, along with Leith and Cheng, describe in an article published in Optics Communications, Opt. Comm. 48, 98 (1983), which is incorporated by reference herein, the idea of combining lenticular photography with multiplex holography. The result is a hologram having a substantial vertical raster line effect.
In the present invention a method and apparatus are disclosed which solve all of the holocoder deficiencies, while at the same time bringing holographic picture taking out of the laboratory and into the hands of unsophisticated users.
Accordingly, it is an object of the invention to provide a recording camera for simultaneously photographing a sequential series of two-dimensional images in incoherent light and a hologram construction apparatus using coherent light to convert the relative parallax information obtained from each of the images into a three-dimensional hologram.
It is an additional object of the invention to provide a camera means to photograph any kind of scene in ordinary incoherent light which is easy to use and functions similarly to a conventional camera, the resulting image recorded being adaptable to constructing a hologram having acceptable parallax properties.
It is yet an additional object of the invention to provide a hologram construction apparatus employing coherent light which utilizes the two-dimensional images produced by the camera to produce a rainbow hologram in one simple step.
It is a further object of the invention to provide an imaging system which is of high quality optical properties.
It is yet a further object of the invention to provide a focusing lens system that allows for sharp image recording and simultaneously reduction in optical grain noise.
It is still an additional object of the invention to provide an imaging system which does not suffer from a dot matrix appearance or a grid line appearance.
It is yet a further object of the invention to provide an optical imaging system which prevents optical cross-talk and allows control over the f-stop, and, accordingly, depth of field.
It is still a further object of the invention to provide an optical imaging system having an achromatic and astigmatic compound lens arrangement.
These, and additional objects, advantages, features, and benefits of the invention will become apparent from the following specification.